Is your job site right for a sound foundation?
Perhaps one of the most important aspects of a building is selecting an appropriate site for development. Just because a site can be bought or leased does not mean it is necessarily suitable for development.
It is critical to evaluate and understand the many conditions of any site being considered for a building’s constructability and usage. A successful site feasibility study can appraise whether a future building site is viable or not, and therefore worth considering. It includes many variables that must be taken into account to evaluate a site’s positive and negative components.
“Site evaluation for a project is often based on access, grading, staging area, location, climate, code compliance, architectural review requirements and costs,” says Charles Hendricks, AIA, CSI, CDT, CAPS, LEED AP BD&C, sustainability director and architect at The Gaines Group, Harrisonburg, Va. “The specific climate the building is located within will impact the insulation and HVAC solution most appropriate for the building, along with the energy efficiency goals of the client.For instance, we used a transpired solar collector on the south face wall of one of our projects since we did not have shading from trees and no humidity control requirements for that particular project. Specifically for a metal building project, it is important to understand the climate implications, regulatory restrictions, availability of roads for delivery, overhead structures, such as bridges and overhead power lines, for the delivery of structural components between the site and the manufacturer. Site access may be impacted by availability of particular cranes, ability for them to arrive at the site and quality of the existing roads.”
The nature of pre-engineered buildings as a “package” makes their construction and site feasibility requirements different from conventional structures. “Typically the components for a conventional structure arrive on-site as needed, so there is less site space required for shake out and storage,” says Arthur E. Hance, president of Hance Construction Inc., Washington, N.J. “Often, a pre-engineered building arrives on-site in one or more closely spaced shipments. Space must be allocated for shake out of structural steel used early in the assembly process, while an area must be designated for the safe storage of roof and wall panels that will be used later in the process.” A detailed survey of the physical condition of any potential construction site is a large part of a site feasibility study.
It can predict the potential work and associated costs of a proposed project to ensure the correct approach to development is taken. It can protect against problems like legal claims and even specify mitigative procedures. Visual observations, notes, videotaping and other diagnostic devices can produce survey documentation to provide detailed information on:
• Existing buildings (including valuation, measured surveys, structural surveys, structural investigations, condition surveys and demolition surveys)
• Geological and geotechnical aspects
• Topographical aspects
• Contamination aspects
• Environmental aspects
• Archaeological aspects
• Traffic and transport aspects
• Local climate
• Flood risk
• Air quality
• Historic use
• Boundary surveys
• Structural surveys (including retained structures, underground structures and obstructions)
• Railway and tunnel search
• Asbestos and other hazardous materials surveys and registers
• Fire hydrants
• Wireless networks and satellite reception
• Electrical infrastructure and capacity
• Gas network infrastructure and capacity
• Foul sewers and drains infrastructure and capacity
• Existing water supply infrastructure and capacity
Hendricks’ colleague at The Gaines Group, principal architect Raymond E. Gaines, AIA, FCSI, CCS, also stresses the need for a site feasibility assessment, saying even examining the air on a potential site should be done. “Additional consideration needs to be given to proximity to potential sources of corrosive air pollution, acid rain or salt spray,” he says. “Under certain circumstances, it Before construction starts, a soil study can determine foundation stability and prevent foundation failure.
(Photo courtesy of ACI Consulting) is advisable to clad a metal building in something other than metal panels, or substitute a panel that has a finish with a higher-than-normal corrosion resistance. Taking these steps can prevent premature failure and ensure attractive, cost-effective buildings for years to come.”
The dirt on soil evaluation
Soil is a significant part of any building’s foundation and can vary in type, composition and strength. A mixture of organic, inorganic and living materials, it’s formed over long periods of time by erosion, water movement, extreme temperature changes and other environmental factors.
Topography can have a dramatic effect on the size and type of cranes and man lifts employed on a project. “If there are dramatic grade changes adjacent to the subject building it may require staging cranes and man lifts further from the structure,” says Hance. “This increased distance can add substantial cost for larger equipment and in some cases requires cranes and lifts that require substantial advance scheduling. If a thorough pre-construction survey is not performed, the wrong equipment can be scheduled and when the realities of the site are discovered, it is often too late to mobilize the correct equipment. This can lead to a dangerous situation where the original equipment is used in an unsafe fashion to try and keep the project on schedule.”
There are five basic soil types: gravel, sand, silt, clay and organic. Some soils are very strong and can support significant weight. Others are weak and compress under light loads. If a building’s foundation is not designed to the soils’ carrying capacity, then they will fail and so will the building. Because a building’s integrity depends so much on the stability and strength under loading of the soil or rock underlying its foundation, a primary component of a site feasibility study is a successful soil test. Soil tests are vital to site feasibility for all building types, and help prevent undue settling and collapse. Once completed, a soil test can visually display soil composition in any given location. The soil profile provides a graphical cross-section of soil layers, starting at the top with ground level and ending at the bedrock below the soil. Before construction starts, a soil study can determine foundation stability and prevent foundation failure by ascertaining soil strength, density compaction, drainage and contamination. Without a soil study, a building can become dangerous even in a small amount of time, or a foundation can be made “too strong” and not profitable. Without a soil survey to predict them, undetected gaps in foundation structures are almost irreparable. “Rigid frame metal buildings require careful soil studies prior to foundation design to accommodate horizontal thrust and potentially higher-thanusual vertical reactions,” says Gaines.
The range of soils across a single site can vary and all should be fully assessed. Soil on top of the ground may not be identical to soil 20 or even 10 feet below the surface. Certain clay soils are highly expansive and contractive; they can swell and shrink in response to moisture content. Standing a foundation on them could result in cracks where the clay has expanded and pushed the foundation up or in because the expanding soil has exerted several thousands of pounds of pressure upwards or outwards.
A potential job site with too much organic soil in it can represent a significant problem for a building foundation. Organic matter is the partially decomposed remains of soil organisms and plant life including lichens and mosses, grasses and leaves, trees, and all other kinds of vegetative matter. While being a plus for gardeners, organic soil is not structurally sound and shouldn’t be used for foundation bearing.
A geotechnical soil test analyzes the proportions of sand, silt and clay together with the soil’s structure and organic matter content. Soil analysis can be performed by geotechnical laboratories via precise, automated equipment, and even on-site. One test involves boring into the soil with narrow-diameter tubes that are punched or pushed through the soil until the tube is filled with sampling material. Lab tests on the undisturbed samples can determine soil composition and minerals. Compaction tests are critical in determining if clay soils are compatible with building, what kind of equipment should be used to compact the soil and how much compaction is required before pouring the foundation.
In addition to compaction testing, some other soil tests include:
• Water content testing
• Void ration testing
• Bulk density testing
• Shear strength testing
• Consolidation testing
• Soil classification services
• Atterberg limits testing
• Hydrometer testing
• Sieve analysis
• Triaxial shear testing
• Nuclear densometer testing
• Bearing capacity testing
These measurement techniques produce information that can:
• Determine clay, silt and sand fractions to classify soil texture
• Evaluate the transport environment for sediments
• Assess potential for contaminant retention within sediments
• Assess the potential uptake of ions within a soil
• Monitor surface charge (i.e., as part of contaminant removal)
• Evaluate particle-to-particle interactions
• Assess particle packing, porosity and permeability
• Evaluate aggregate structures
In addition to receiving information from these soil testing techniques, there is free and useful assistance available elsewhere. “County soil survey information is available for most counties,” says Robert L. Parsons, assistant professor of civil and environmental engineering at the University of Kansas, Lawrence, Kan. “These surveys can indicate if soil conditions are a major concern, probably a concern or not a concern, for example, although they are not a substitute for an engineering investigation.” Even after discovering a potential construction site has weak soil, buildings may still be built there. If the native soil is unsuitable or inadequate for building, it can be blended with or replaced by soil from another source. Also, “If a structure must be built on a site with poor soils, construction options exist that can minimize or eliminate soil shrinking and swelling for an additional cost,” Parsons says.
Hendricks stresses that site feasibility should be initiated at the very conception of a project and its information should be utilized throughout construction. “While many factors go into creating a successful project, proper planning on the front side often will reduce surprises during the design and construction process,” he says. “As an architect, I am a big fan of systems that reduce the number of oversights and exclusions during design. Having a comprehensive checklist will allow you to guide a client as they are making decisions about sites for their upcoming projects in a fashion that is easy to navigate and evaluate.”